1. Field of the Invention
The present invention generally relates to a microelectromechanical system (MEMS) structure and a fabricating method thereof, and in particular, to an MEMS structure having a protection ring and a fabricating method thereof.
2. Description of Related Art
A microelectromechanical system (MEMS) is a microelectromechanical device fabricated in a microminiaturized package structure, and the fabricating technique thereof is quite similar to the technique of fabricating integrated circuits (ICs). However, interactions, for example, about mechanics, optics, or magnetic force between the MEMS device and surrounding environment are more than that of the conventional IC. The MEMS device may include micro-sized electromechanical components, such as motors, pumps, valves, switches, capacitors, accelerometers, sensors, capacitive sensors, pixels, microphones, or actuators, etc. The electromechanical components, which are designed based on capacitance principles, usually work out by the coaction between the mechanical structure and the semiconductor device (e.g. IC), thereby resulting in the displacement of the structure to achieve the anticipated effect.
In general, the MEMS is fabricated by forming the devices on a silicon wafer using the semiconductor process technology, and then the MEMS may be integrated with the IC in a manner of a single block. Along with the rapid progress of the semiconductor process and packaging technique, the MEMS are designed in the concept of miniaturization and integration. In order to satisfy the demands, it is the trend to develop the fabrication of the MEMS that can be integrated with the fabrication of the IC chips through the semiconductor process.
However, the conventional process of the MEMS is usually fabricated after the back end of the semiconductor process is finished. In other words, after accomplishing the fabrication of the IC chip, a plurality of thick polysilicon layers are deposited in the region where MEMS to be formed, so as to form the structure of the MEMS device. The MEMS device easily suffers from the stress issue due to the structure formed from polysilicon material. Moreover, polysilicon material is prone to bend under an influence of continuously repeating mechanical stress, such that the life of the device is diminished and the performance thereof is unsatisfying. Although the deposition of the polysilicon layer is a common semiconductor process, polysilicon material will not be formed in the back end of the general semiconductor process. Accordingly, the formation of the MEMS structure utilizing polysilicon as material needs additional procedures, and the fabricating steps and the cost are raised. In practical proceeding, the MEMS structure utilized polysilicon material is also limited to the thickness of the polysilicon layer deposited, which makes a great impact on the device.